(1) Field of the Invention
The present invention lies in the technical field of standby instruments for piloting an aircraft. The present invention relates to a standby instrument that combines several types of function, i.e. it supplies flight information, power or torque margin information, and it also provides piloting assistance. The standby instrument is more particularly for use on a rotary wing aircraft. The invention also provides a method of operating the standby instrument.
(2) Description of Related Art
In the event of a main information system failing, a standby instrument acts to take its place and to provide the pilot with information that is essential and considered as being critical in terms of flight safety. The pilot can thus continue to pilot the aircraft in complete safety in spite of the failure of the main information system. The critical information generally provided by the standby instrument relates to the forward speed of the aircraft, its altitude, its attitudes, and also its heading. The term “attitudes” should be understood as meaning its Euler angles in roll and in pitching.
Such a standby instrument incorporates all of the resources it needs, in particular one or more inertial and pressure sensors together with one or more display units, conventionally a screen. The standby instrument is independent of the main information system. Such a standby instrument is commonly referred to as an integrated standby instrument system (ISIS) or as an integrated electronic standby instrument (IESI).
In the event of a failure of a main piloting assistance device, another instrument can take its place and provide the pilot with partial assistance, mainly short-term stabilization concerning angular speeds in roll, pitching, and yaw. This short-term stabilization is intended to counter the aircraft beginning to present angular speeds in the form of drift or oscillation about the roll, pitching, and yaw axes. Such an instrument incorporates an inertial sensor of the gyroscopic type, and calculation means for determining the control relationships for stabilizing the aircraft in this way.
Certain aircraft may also include a device that provides information about the management of the power of their engines. Such a device generally provides a first utilization limit for the engine(s) above which the pilot can use the aircraft for a limited length of time only, and it provides an engine utilization margin that corresponds to the power or torque margin that is available relative to said limit. By way of example, such devices are described in documents FR 2 749 545 and FR 2 756 256. Such an instrument is referred to as a first limitation instrument. This power or torque limitation is a function simultaneously of operating parameters of the engine(s) and of flight conditions.
In the event of a failure of said first limitation instrument, certain rotary wing aircraft make use of marking on the collective pitch control. This marking indicates a safe zone to the pilot, i.e. a zone in which the pilot can operate without running the risk of exceeding the utilization limit of the engine(s) of the aircraft. However, under such circumstances the pilot has no realistic idea about the power or torque margin at the engine(s) that is available as a function of various flight conditions.
On principle, in order to satisfy constraints imposed by regulations concerning any critical piloting function for the aircraft, a standby instrument must guarantee independence from the corresponding main instrument and thus mitigate any errors of design or production that might be shared in common. Having a standby instrument that is independent guarantees that the failure of the main system will not affect this standby instrument directly. The term “failure” is used to designate any behavior that does not comply with expectations for its function. Dissimilarity, which consists in using components in the standby instrument that are different from the components making up the main system, serves to reduce the risk of a failure that affects the main system also affecting the standby instrument, and thus contributes to this independence of the standby instrument relative to the main instrument. By way of example, these differences may be sensors that make use of a different technical solution, or calculation means that have a different architecture.
These various standby instruments that perform various functions can be found nowadays on a single aircraft, but they remain completely independent of one another. Each system has its own sensors and one or more specific calculation means.
Document U.S. Pat. No. 3,752,420 describes a system used in an autopilot in order to stabilize the behavior of the aircraft, in particular relative to the pitching movement of the aircraft. That system makes use of information coming from two different inertial sensors that provide information about position and speed about the pitching axis. The system filters this information and then delivers a signal that makes it possible in particular to stabilize the aircraft by means of the autopilot. That system is also capable of detecting an error in the information delivered by one of the sensors, in which case it adapts the piloting relationship of the autopilot in order to conserve stable behavior for the aircraft.
Document FR 2 784 457 describes standby instruments having pressure and inertial sensors, and also electronic measurement systems and calculation means. The standby instruments are thus capable, in the event of a failure a main information system, of providing critical information to the pilot, i.e. the forward speed of the aircraft, its altitude, and its attitudes, while incorporating corrections in order to improve the accuracy of that information. In particular, on the basis of the information from the sensors, that system is capable of determining the aerodynamic angle of attack of the aircraft and its Mach number, and it is capable of deducing therefrom a correction factor that then serves to improve the accuracy of the critical information.
In addition, document FR 2 855 303 describes a standby display device that is capable, in the event of a failure of the main display device, of supplying various kinds of information as selected by the pilot. Three configurations are possible. In a first configuration, only piloting information such as forward speed of the aircraft, its altitude, and its attitudes is displayed on a screen. In a second configuration, only navigation information such as the heading of the aircraft and its position relative to a theoretical route is delivered to the pilot. Finally, in a third configuration, the screen displays both piloting information and navigation information.
Also known is document FR 2 903 787, which describes a standby device that acts in the event of a failure of a main device to deliver critical information about forward speed, altitude, and attitudes to the pilot of the aircraft. That device conventionally incorporates inertial and pressure measurement sensors together with calculation means and display means. The particular feature of that device lies in its display mode, which forms part of a so-called “head-up” viewing system.
Furthermore, document FR 2 919 066 describes a standby instrument that acts, in the event of a failure of a main device, to deliver critical information about forward speed, altitude, and attitudes to the pilot of the aircraft. That standby instrument conventionally incorporates inertial and pressure measurement sensors together with calculation means and display means. Once more, the display mode used is a head-up viewing system, but the particular feature of that instrument lies in displaying a speed vector of the aircraft. The calculation means are capable of determining the speed vector solely on the basis of the information from the inertial and pressure measurement sensors.
Also known is document US 2007/164166, which describes a standby instrument capable of taking the place of a primary flight control instrument of an aircraft. That standby instrument includes in particular one or more sensors, calculation means, and information transmission means. In addition, that standby instrument is connected to the flight actuators of the aircraft. In the event of a failure of the primary flight control instrument, the standby instrument serves to control those flight actuators and thus enables the aircraft to continue its flight safely.
Document FR 2 924 213 describes a standby instrument including sensors, means for processing measurements from the sensors, radio communication management means, and a display screen. That standby instrument can thus display both primary and flight critical information and also radio communication and/or radio navigation data.
Finally, document EP 2 301 844 describes a piloting assistance method and device for an aircraft having at least two engines. In the event of a failure of a first limitation indicator, that piloting assistance method and device serve to maintain each engine-monitoring parameter below a predetermined threshold.